One of the leading challenges facing designers of wireless products is achieving acceptable battery life without requiring large batteries that impact the weight and form factor of the product. A conventional solution to this problem is to place the wireless device in a very low power sleep mode, or standby mode, when it is not in use. In this case, the challenge is to accurately determine when the device is in use and when it can safely be put in sleep mode, and to then transition between sleep and active modes quickly enough for the power management activity to be undetectable to the user, while maximizing power savings.
In a wireless mouse input device, recent movement of the device is a good indicator of whether or not the mouse is in use. Other applications where recent movement is a good indicator of device use include wireless game-pads, remote controls, and many other wireless and cabled handheld devices that are battery or externally powered.
A significant challenge facing designers of wireless mice and other wireless products is battery life. Mice typically use optical sensors to detect mouse motion. The optical sensor and associated surface illumination are the largest consumers of power.
A typical wireless optical mouse has a five stage power-saving algorithm, as shown in FIG. 1. In a first stage, the mouse is in an active state 12, where mouse motion has been detected within a preceding one second interval. In active state 12, the optical sensor is fully active and capable of detecting movement with maximum precision and minimum latency.
In a second stage, the mouse is in a semi-active state 14. State 14 persists from a time one second since the last mouse motion was detected until ten seconds since the last motion was detected. During the second state 14, the optical sensor captures images less frequency and turns off the surface illumination when not capturing images. This results in increased latency in motion detection and much less precise detection of mouse movement.
In the third stage, the mouse is in the ‘standby 1’ state 16. This stage begins ten seconds after the last motion was detected and ends ten minutes later. In other words, the most recent mouse movement was more than ten seconds ago but less than ten minutes earlier. In state 16, the optical sensor and surface illumination are completely turned off for most of the time, but are turned on several times per second to check for motion.
After ten minutes in the standby state 16, the mouse moves into a fourth stage. In stage 4, the mouse transitions to (is in) the ‘standby 2’ state 18. This is where the most recent mouse movement occurred ten or more minutes earlier. State 18 has similar operation to the previous state 16, except that the sensor and illumination are turned on less frequently, typically once per second. After thirty minutes of no mouse activity, the mouse transitions to the fifth stage, where the mouse is in the ‘sleep’ state 20 and can only be woken by pressing a button.
This scheme has the following disadvantages. A first disadvantage is that the mouse is still consuming significant current for 30 minutes after a last mouse movement. A second disadvantage is that in standby modes, the user has to move the mouse for a perceptible period of time before the mouse wakes up and starts controlling the computer. Another disadvantage is that the user has to wake the mouse up in sleep mode by pressing a button.
Various alternative conventional methods of mechanically detecting motion are available. These methods can automatically wake up the mouse when it is asleep, thus eliminating the two standby modes. These alternative methods vary in cost and generally are only suitable for use in higher end mouse devices.
One such configuration includes a number of conductive balls housed in a small chamber. A plurality of electrical contacts make contact are located inside the chamber. Motion of the object containing the chamber causes the balls to move around making and/or breaking electrical connections between the electrical contacts. An electrical circuit detects movement of the device by identifying changes in the make/break state between the contacts.
Disadvantages of this system includes insensitivity to slow or small mouse movements. For example, a large acceleration is needed to activate the mouse. Even if moderately priced, in an application where every penny counts, the cost of this conductive ball arrangement may still be too high.
Referring to FIG. 2, a conventional wireless optical mouse comprises three Printed Circuit Boards (PCBs). A first PCB 22 contains a microcontroller, radio components and power management components. A second PCB 26 contains an optical motion sensor and a surface illumination LED. A third PCB 24 contains micro-switches activated by pressing mouse buttons, and possibly a sensor that detects rotation of a mouse scroll wheel.
The first PCB 22 is typically mounted towards the top of a mouse enclosure, while the second and third PCBs 26 and 24 are mounted on the base of the mouse enclosure. The top PCB 22 overlaps each of the lower PCBs 26 and 24 and connects to the lower PCBs 26 and 24 using pin headers 28 that are approximately 10 millimeters (mm) in length.
It would be desirable to have a low cost scheme for detecting small accelerations in electrical devices.